A conventional electrical appliance such as an oven is normally connected with a power cord to an AC electrical main to conduct current through a resistive heating element. A bimetallic control is commonly used to control the current flow in response to temperature. The bimetallic control is located near the heating element, or in some part of the appliance housing where it can respond to excessive temperature, to assume an open, non-conductive state.
Various semiconductor switches capable of conducting large currents are known. However, bimetallic devices have remained the control of choice for AC-operated electrical appliances despite limited accuracy and limited functionality. Use of a semiconductor switch would require a temperature sensor and a control circuit responsive to operation of the sensor. These are normally operated with DC voltages, and, in any event, not at voltage levels associated with electrical mains. Transformers and regulated voltage supplies would normally be used to reduce voltage levels and provide DC operating voltages. Although very sophisticated solid-state control can then be implemented, the cost would far exceed that of using a simple bimetallic strip.
The present specification addresses such problems and provides inter alia an electrical heating appliance which incorporates a relatively low-cost current control circuit based on a semiconductor switching element.